creating polygon tips
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8/3/2019 Creating Polygon Tips
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Tips on Creating Polygons in ArcGISTable of Contents
How to Make a Polygon
Basic Steps
Create a Layer
Creating Polygons
Basics
Snapping
Create New Feature
Auto Complete Polygon
Dealing with Gaps and Slivers
Prevention
Fill in Gaps
Remove Slivers
1. How to Make a Polygon
Basic stepsCreate a Layer
• Create a layer dedicated to your polygons.
[ArcCatalog>find your folder>File>New>Shapefile]
• When creating a Shapefile for polygons, it should be
o Named
o Feature type = polygon
o Import the same coordinate system [Edit>
Import>then choose an air photo you’re going to
draw polygons on]
• Now return to ArcMap and add the Shapefile you just
created as a new layer and you’re good to go!Creating Polygons
Basics
• Make sure your polygon editing toolbar is there
[Tools>Editor Toolbar]
• Then “Start Editing” [Click “Editor” on the Editor
Toolbar>Start Editing>Select the folder your shapefile is
in]
Snapping
• Turn it on!
[Click “Editor” on the Editor Toolbar>Snapping]
• Once you see the Snapping menu, select “vertex”, “edge”and “end” for each of the layers (e.g. a boundary, and your
polygon layer, so the borders of your polygons line up).
• Activate drawing tool [Click the pencil]
• IF you have multiple polygon Shapefile layers, make sure
that you select the correct Shapefile to draw on by selecting
the “Target” dropdown menu inside the Editor Toolbar.
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• There are plenty of ways to draw a polygon, but the basic
ones are often the best. The two most common ones are
explained below.
Create New Feature
• This is the default setting, and is the most common methodof creating a polygon.
• Create the outline of the shape you want, and double click
at the final corner (i.e. not the first point)
• See Create New Feature Photo Procedure
Autocomplete Polygon
• When to use: when there is an awkward edge resulting
from many random polygons. Rather than follow the dips
and turns of that edge, use Autocomplete Polygon
• Make sure both your start and end points are inside a
polygon (they don’t have to begin and end in the same
polygon)• See Autocomplete Photo Procedure
Note: Use both methods together to minimize gaps between
polygons. If you get gaps anyway, see here.
2. Dealing with Gaps and Slivers
Prevention
Make sure pretty much every Snapping category for each layer is
selected (i.e. Vertex, Edge, End). This ensures that when you are
hovering your cursor, about lay down a new point, the cursor is
attracted (i.e. snapped) to the boundaries of previous polygons.
Use Auto-Complete Polygon to fill in a complex edge rather than
try to follow the edge with Create New Polygon.
Fill in Gaps
Use the Integrate geoprocessing tool to remove gaps by merging
the polygons surrounding a gap together
[ArcToolbox>Data Management>Feature Class>Integrate]
• You’ll be asked for the desired XY tolerance when using
Integrate, but if you decide not to specify, the XY
Tolerance will be a default of 0.001. Setting a smaller
number will Integrate to seek smaller gaps to fill in. If
entire polygons disappear, your XY Tolerance is too big. In
the lower right of the ArcMap browser, it should show
what units you are using. Make sure the Tolerance units are
the same.
Select Modify Feature under the Task dropdown menu. This
allows you to double-click a polygon and see all the end points. If
you hover the cursor over a re-emerged end point, the cursor
becomes a compass rose looking icon. Click the end point at that
time and maneuver to new location. Double-clicking outside the
polygon will revert to the modified polygon. This is a tedious way
to get rid of gaps, so be sure to prevent them instead.
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Remove Slivers
Use the Eliminate geoprocessing tool to merge slivers into
neighboring polygons.
[ArcToolbox>Data Management Tools>Generalization>Eliminate]
Create New Polygon: Photo procedure
Fig 1.1 Draw a polygon with as many points as you like. The upper left corner is the
starting corner, and the lower left corner is the final point. Be sure to double click at that
final point.
Fig 1.2 Voila!
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Autocomplete Polygon: Photo procedure
Fig 2.1 Here is that awkward edge created by polygons
Fig 2.2 Autocomplete polygon will fill in that awkward edge for you. Make sure start and
end points are inside a polygon, and the awkward edge you’re filling in is contiguous.
Fig 1.3 Voila!